Dealing with environmental concerns has conventionally been focused on emission from automobiles or factories because an amount of the emission from them is large. In recent years, however, improving an amount of emission from shipping vessels has been desired as well in spite of good energy efficiency and relatively a small amount of emission. In order to reduce an amount of sulfur oxide (SOx) and black smoke emitted mainly from ships, a sulfur content in marine fuels is being regulated (refer to Non Patent Literatures 1 and 2).
The sulfur oxide and particulate matter are attributable to sulfur in fuels (Non Patent Literature 1). Thus, using fuels including 0.5 mass % or less, currently 3.5 mass %, of the sulfur content for the ships sailing in the general sea area is obligated in 2020 or 2025. Additionally, using fuels including 0.1 mass % or lower of the sulfur content for the ships sailing in the sea and in the gulf coast near California and Europe is obligated.
A C-type heavy fuel oil composition, which is widely used as marine fuels, can be subject to the above regulation of the sulfur content. However, the C-type heavy fuel oil composition is required to satisfy necessary performance in terms of not only the sulfur content but also other properties, such as ignitability, combustibility and low-temperature fluidity. Accordingly, various techniques therefor have been proposed until now.
For example, in Patent Literature 1 (Japanese Patent Laid-Open No. 2014-51591), a C-type heavy fuel oil composition having an ignitability index I, as derived from a specific equation, of not less than 0 and less than 15 is proposed.